1. Field of the Invention
This invention relates to a system for reducing vehicle emissions in a vehicle having an internal combustion engine and a catalytic converter, and in particular to a system and method for rapidly bringing the catalytic converter to light-off temperature by introducing a hydrogen containing fluid into the exhaust stream.
The invention also relates to a system for reducing vehicle emissions by introducing a hydrogen containing fluid into the exhaust stream, and in which the hydrogen containing fluid is in the form of hydrogen gas generated by an on-board electrolysis device or reformer powered by the heat of the exhaust stream, for example by a thermo-electric generator secured to or integral with the catalytic converter. The hydrogen gas may also be added to the fuel intake to boost fuel efficiency and further reduce emissions.
The invention further relates to a system for utilizing waste heat generated by an internal combustion engine to generate hydrogen for use by the internal combustion engine or to reduce emissions.
Finally, the invention relates to a method for reducing emissions and conserving energy, and to a catalytic converter capable of reducing emissions and at the same time improving fuel efficiency.
2. Description of Related Art
In a conventional vehicle, 70% to 80% of emissions occur during the first 100 seconds following a cold-start. The reason is that the catalytic converter does not begin operating to reduce emissions until the catalyst has reached a “light-off” temperature. As a result, it has previously been proposed to pre-heat the catalytic converter, so that when the engine is started, the catalytic converter immediately begins reducing emissions. These proposals all involve electrically heating the converter using a resistance element, as described by way of example in U.S. Pat. Nos. 6,613,293; 6,562,305; 6,168,763; 5,948,504; and 5,852,274. Such heaters have the advantage of decreasing emissions not only during a cold start, but also during idling in the case of cooler running engines such as diesels. However, they have the disadvantage of increasing the electrical load on the engine, resulting in decreased fuel economy.
A partial solution to the problem of heating a catalytic converter without decreased fuel economy is proposed in U.S. Pat. No. 5,968,456. According to U.S. Pat. No. 5,968,456, the device that pre-heat the converter is a thermo-electric generator that generates electricity from the heat carried by the exhaust stream when pre-heating is not required. As a result, there is a net energy savings since the electricity generated by the thermo-electric generator can be stored in a battery and used not only to power the heater, but also electrical systems and devices.
Other proposals for converting waste heat emitted by an internal combustion engine or carried by the exhaust stream or engine coolant are found in U.S. Pat. Nos. 6,605,773; 6,172,427; 5,625,245; 4,753,682; and 4,673,863, while U.S. Pat. Nos. 5,753,383 and 4,161,657 propose the inclusion of thermoelectric generators in hydrogen powered vehicles that includes both a burner module and a fuel cell. For the most part, these systems promise significant energy savings (for example, around 80% of the energy output of an internal combustion engine is in the form of heat). However, use of the energy to pre-heat a catalytic converter at start-up, as proposed in the above-discussed U.S. Pat. No. 5,968,456, is not the best use for the re-captured energy, and in fact negates a significant portion of the energy savings since (i) resistance heating is not very energy efficient, and (ii) the added electrical load on the engine at start-up requires a much higher system energy capacity, including higher capacity batteries. The need for higher capacity batteries increases the weight of the vehicle and decreases fuel efficiency.
None of the previous proposals for using electric resistance elements, and/or a thermo-electric generator, to pre-heat a catalytic converter involves injecting a hydrogen-containing gas into the converter in order to initiate an exothermic reaction that instantaneously heats the catalyst. It is of course known that hydrogen can cause heating of a catalyst (see, e.g., U.S. Pat. No. 6,231,831, which discloses a heating of a catalyst-coated membrane in a methanol reformation system), but the principle has not previously been applied to the catalytic converter of a vehicle emissions reduction system.
Additional background on the generation and use of hydrogen in vehicles is found in U.S. Pat. No. 6,659,049 (condensation in exhaust converted to hydrogen for mixture with hydrocarbon fuel); U.S. Pat. No. 6,559,551 (hydrogen generation for a fuel cell); U.S. Pat. No. 4,368,696 (hydrogen and oxygen generation to supplement gasoline fuel); and U.S. Pat. No. 6,516,615 (compressed hydrogen fuel that obtains work from both decompression and burning).